Transcriptome profiling of the Pacific oyster (Crassostrea gigas) suggests distinct host immune strategy in response to Vibrio alginolyticus infection

Bacterial infection is a serious challenge for oysters, which brings various disease problems to oyster culture. To better understand the immune response to bacterial infection, we performed RNA-seq to profile the transcriptome of gill tissue in the Pacific oyster (Crassostrea gigas) at short-term (6 h) and long-term (48 h) stages after Vibrio alginolyticus infection. A total of 1534 and 2483 differentially expressed genes (DEGs) were identified at short- and long-term stages after infection, respectively. Gene ontology (GO) analysis showed that the identified DEGs were significantly enriched in GO terms of stress response, ion transport, signal transduction and other biological processes. Notably, we observed that the immune strategy was altered in the C. gigas in response to Vibrio infection. In the short-term stage, most of the immune-related genes in C. gigas were down-regulated, and the immune response was low and may be suppressed. While in the long-term stage, large-scale immune-related genes associated with ion channels were activated and immune system was boosted. Distinct sets of immune-related genes with different functions were identified at short-term and long-term stages. Differences in these genes suggested the alteration of immune strategy in the C. gigas in response to Vibrio infection. This work provides valuable resources for better understanding of immune response to bacterial infection and will be important for disease monitoring and disease resistance breeding in the oysters.